Preparation, characterization, surface modification and redox reactions of silver nanoparticles in the presence of tryptophan

The synthesis and characterization of water-soluble dispersions of Ag nanoparticles by the reduction of AgNO(3) using tryptophan under alkaline synthesis conditions are reported. The Ag nanoparticle formation was very slow at low concentration and rapid at extremes. For surface modification and redox reactions, manipulating the interparticles interaction controlled the size of Ag nanoparticles aggregates. Our results suggest that the replacement of the BH(4)(-) ions adsorbed on the nanoparticle surface by tryptophan destabilizes the particles and further caused aggregation. A mechanism is proposed for the formation of silver nanoparticles by tryptophan. The experimental results are supported by theoretical calculations. The Ag nanoparticles were characterized by UV-vis absorption, dynamic light scattering and transmission electron microscopy techniques.     

Preparation and characterization of stable monodisperse silver nanoparticles via photoreduction

Silver nanoparticles were synthesized by UV irradiation of [Ag(NH₃)₂]⁺ aqueous solution using poly(N-vinyl-2-pyrrolidone) (PVP) as both reducing and stabilizing agents. The formation of silver nanoparticles was confirmed from the appearance of surface plasmon absorption maxima around 420 nm. It was found that the formation rate of silver nanoparticles from Ag₂O was much quicker than that from AgNO₃, and the absorption intensity increased with PVP concentration as well as irradiation time. The maximum absorption wavelength (λ_max) was blue shift with increasing PVP content until 8 times concentration of [Ag(NH₃)₂]⁺ (wt%). The transmission electron microscopy (TEM) showed the resultant particles were 4–6 nm in size, monodisperse and uniform particle size distribution. X-ray diffraction (XRD) demonstrated that the colloidal nanoparticles were the pure silver. In addition, the silver nanoparticles prepared by the method were stable in aqueous solution over a period of 6 months at room temperature (25 °C).     

Preparation and characterization of silver nanoparticles by chemical reduction method

Silver nanoparticles were prepared by the reduction of AgNO(3) with aniline in dilute aqueous solutions containing cetyltrimethlyammonium bromide, CTAB. Nanoparticles growth was assessed by UV-vis spectroscopy and the average particle size and the size distribution were determined from transmission electron microscopy, TEM. As the reaction proceeds, a typical plasmon absorption band at 390-450nm appears for the silver nanoparticles and the intensities increase with the time. Effects of [aniline], [CTAB] and [Ag(+)] on the particle formation rate were analyzed. The apparent rate constants for the formation of silver nanoparticles first increased until it reached a maximum then decreased with [aniline]. TEM photographs indicate that the silver sol consist of well dispersed agglomerates of spherical shape nanoparticles with particle size range from 10 to 30nm. Aniline concentrations have no significant effect on the shape, size and the size distribution of Ag-nanoparticles. Aniline acts as a reducing as well as adsorbing agent in the preparation of roughly spherical, agglomerated and face-centered-cubic silver nanoparticles.     

Preparation and characterization of a novel nanocomposite: silver nanoparticles decorated cerasome

In this study, a novel artificial hybrid vesicle, nano silver particles decorated cerasome were fabricated through sol–gel and self-assemble methods as well as in situ reduction. Samples were characterized in terms of hydrodynamic size and surface morphology via dynamic light scattering as well as scanning and transmission electron microscopies. Analysis through energy dispersive X-ray spectrometer proved the existence of silver particles. Due to the high morphological stability of cerasome, Silver nanoparticles with a size of about 5–10 nm can be deposited on the surface without any stabilizers. The UV spectra revealed a single symmetric extinction peak at 406 nm, confirming the spherical shape of the synthesized silver nanoparticles. Several reducing agents were screened before confirming sodium borohydride (NaBH₄). Comparison of different NaBH₄/lipid ratios (K_{NaBH4/cerasome-forming lipid}) was then carried out in order to ascertain its effect. Investigation of the stability of this hybrid vesicles was carried out, indicating that it can be stored at 4 °C for at least 3 months without any morphological change. Results demonstrated that this hybrid vesicle has excellent morphological stability, which impart it significant potential for various applications such as being an antibacterial material and a radio sensitization agent.     

Formation of silver nanoparticles in formamide:water mixtures: a radiolytic study

The pulse radiolysis of FA and FA:water solutions was studied in the absence and presence of redox indicator 1,1′-dimethyl-4,4′-bipyridinium dichloride (methyl viologen, MV²⁺). The experiments performed in the presence of MV²⁺ have provided strong support to the idea that the first species obtained from the reaction of e_sol⁻ and ^•OH with FA produces radicals that show reactivity towards the MV²⁺. Both the radicals on reaction with MV²⁺ results in the appearance of the well-known intense blue MV^•+ radical absorption signal (λ_max = 395 nm, λ_max = 605 nm). The intermediate radicals formed during radiolysis were used to generate silver nanoparticles.     

Synthesis of silver nanoprisms in formamide

Polygonal (mainly triangular) silver nanoprisms were prepared by reducing silver perchlorate in formamide in the presence of polyethylene glycol (PEG) at room temperature. The reduction of silver ions by formamide leads to the deposition of arrays of triangular shaped silver nanoparticles on the glass walls of the container, accompanied by evolution of CO2 gas. In the presence of poly(N-vinyl-2-pyrrolidone) (PVP) and PEG (1:1), both nanospheres and nanoprisms are formed.     

Preparation,characterization, and antibacterial activity of composite material: Cotton fabric/hydrogel/silver nanoparticles

A new composite cotton fabric with hydrogel containing silver nanoparticles (AgNPs) has been synthesized by two steps, and simultaneous in situ synthesis of AgNPs under visible light irradiation has been performed. The influence of silver nitrate concentration upon the hydrogel and AgNP properties was studied by colorimetric analysis, scanning electron microscopy, and transmission electron microscopy. The antibacterial activities of the composite materials have been investigated against Acinetobacter johnsonii and Escherichia coli in agar medium and meat-peptone broth. The results showed high inhibition activity toward both test cultures which were better expressed against A. johnsonii.     

Green synthesis and characterization of polymer-stabilized silver nanoparticles

Silver nanoparticles (Ag-NPs) were synthesized using a facile green chemistry synthetic route. The reaction occurred at ambient temperature with four reducing agents introduced to obtain nanoscale Ag-NPs. The variables of the green synthetic route, such as acidity, concentration of starting materials, and molar ratio of reactants were optimized. Dispersing agents were employed to prevent Ag-NPs from aggregating. Advanced instrumentation techniques, such as X-ray powder diffraction (XRD), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), ultraviolet–visible spectroscopy (UV–vis), and phase analysis light scattering technique (ZetaPALS) were applied to characterize the morphology, particle size distribution, elemental composition, and electrokinetic behavior of the Ag-NPs. UV–vis spectra detected the characteristic plasmon at approximately 395–410 nm; and XRD results were indicative of face-centered cubic phase structure of Ag. These particles were found to be monodispersed and highly crystalline, displaying near-spherical appearance, with average particle size of 10.2 nm using citrate or 13.7 nm using ascorbic acid as reductants from particle size analysis by ZetaPALS, respectively. The rapid electrokinetic behavior of the Ag was evaluated using zetapotential (from −40 to −42 mV), which was highly dependant on nanoparticle acidity and particle size. The current research opens a new avenue for the green fabrication of nanomaterials (including variables optimization and aggregation prevention), and functionalization in the field of nanocatalysis, disinfection, and electronics.     

Preparation of silver nanoparticles in liquid crystalline systems

Silver nanoparticles preparation and the aggregation stability of the particles was investigated in lamellar liquid crystalline systems. A liquid crystal of HDTABr/pentanol/water was first prepared. The water content was next increased while keeping the mass ratio of HDTABr and pentanol constant. Silver nanoparticles were produced by replacing the aqueous phase by Ag sols of various concentrations (0.5–5×10^–3 mol/l) or by an in situ preparation method, i.e., interlamellar reduction of Ag⁺ ions in the liquid crystalline phase. The stability of the silver nanoparticles was monitored by UV-VIS spectroscopy and TEM. The particle size ranged from 5 to 44 nm. The kinetic of silver nanoparticle aggregation was investigated. The effect of nanoparticles on structural ordering in liquid crystals was studied by XRD measurements and it was established that the lamellar distance (d_L) was only slightly altered. Electronic Publication     

Synthesis, surface modification, and multilayer construction of mixed-monolayer-protected CdS nanoparticles

Herein, we describe a study aimed at synthesizing mixed-monolayer-protected CdS nanoparticles and investigating the reactivity of surface-bound functional groups in order to facilitate the immobilization of nanoparticles on a solid substrate as well as the construction of a three-dimensional nanocomposite. CdS nanoparticles initially prepared by the reverse micelle method were used to modify nanoparticle surfaces with 1-decanethiol molecules by ligand exchange. Subsequently, 11-mercapto-1-undecanol was partially incorporated by a place exchange reaction, thereby providing stable, mixed-monolayer-protected CdS nanoparticles. The nanoparticles obtained at each step were characterized by FT-IR and UV-vis spectroscopy, transmission electron microscopy, and elemental analysis. The reactivity of surface hydroxyl groups was verified by a reaction with isocyanate-bearing molecules that provide carbamate bonds in high yields at ambient temperature. The obtained mixed-monolayer-protected nanoparticles were also successfully immobilized on a glass substrate through a carbamate-bond-forming reaction that could be further utilized for multilayer construction in a layer-by-layer fashion.     

Solubility studies in formamide: III. Solubility product of silver bromate and standard electrode potential of silver—silver bromate electrode in formamide

The solubility and solubility product of silver bromate in formamide in sodium perchlorate solutions have been determined at 25, 30 and 35°C. At these temperatures, the solubilities in pure formamide are found to be 1.837 × 10^?2, 1.967 × 10^?2, and 2.092 × 10^?2 moll^?1, respectively, and the corresponding solubility products are 3.375 × 10^?4, 3.869 × 10^?4, and 4.377 × 10^?4 mol² l^?2. The standard potentials of the Ag(s)/AgBrO₃(s)/BrO^?₃ electrode have been calculated and found to be 0.4997, 0.4948, and 0.4892 V, at 25, 30, and 35°C, respectively. The mean activity coefficients of silver bromate at various rounded molarities of sodium perchlorate solutions, and the standard thermodynamic quantities for the process AgBrO₃(s) → Ag⁺(solvated) + BrO^?₃(solvated) have been calculated at these three temperatures and compared with those for the process AgIO₃(s) → Ag⁺(solvated) + IO^?₃(solvated) in formamide.     

Solubility studies in formamide: II. Solubility product of silver iodate and standard electrode potential of silver—silver iodate electrode in formamide

The solubility and solubility product of silver iodate in formamide in sodium perchlorate solutions have been determined at 25, 30 and 35°C. The solubilities in pure formamide are found to be 2.169 × 10^?4, 2.488 × 10^?4, and 2.943 × 10^?4 mole I^?1, respectively, at these temperatures, and the corresponding solubility products are 4.609 × 10^?8, 6.053 × 10^?8, and 8.448 × 10^?8 mole² 1^?2. The standard potential of the Ag_(s)/AgIO_3(s)/IO₃^? electrode has been calculated and found to be 0.2562 V at 25°C. The mean activity coefficients of silver iodate at various rounded molarities of sodium perchlorate solutions, and the standard thermodynamic quantities for the process AgIO_3(s)åAg⁺ (solvated) + IO₃^? (solvated) have been calculated at these three temperatures.     

Preparation and characterization of porphyrin nanoparticles

The synthesis, characterization, and stability of porphyrin nanoparticles of 20-200 nm diameter presented herein is general for meso arylporphyrins. The elegance of the method lies in its simplicity. This work shows that the agent used to prevent agglomeration can be covalently attached to the dye forming the particle or be part of the solvent system. It also demonstrates that these and other types of dyes with a range of photonic properties do not need to be prepared by inclusion in external matrices or by designed self-assembly a priori. The matrix may severely limit the functionality of the particles in the former case, and at present this size of particle is difficult to achieve via the latter.     

Preparation and surface characterization of polymer nanoparticles designed for incorporation into hybrid materials

We prepared water dispersions of poly(n-butyl methacrylate-st-butyl acrylate) crosslinked core-shell nanoparticles functionalized with different amounts of trimethoxisilane (TMS) groups in the outer shell. The purpose of the TMS groups is to chemically bind the rubbery particles to a nanostructured silica network, using sol-gel copolymerization. Here, we present nanoparticles containing 13 mol % and 30 mol % of TMS groups in the outer shell and compare their surface morphology with particles that do not contain TMS. The particles are prepared by a two-step seeded emulsion polymerization technique at neutral pH. In the first step, we obtained crosslinked seed particles (44 nm in diameter) by a batch process. In the second step, we used a semi-continuous emulsion polymerization technique under starved feed conditions to obtain monodispersed particles of controlled composition and size (ca. 100 nm in diameter). Fluorescence decay measurements were performed in situ on the dispersions, using a pair of cationic dyes adsorbed onto the surface of the nanoparticles: rhodamine 6G as the energy transfer donor and malachite green carbinol hydrochloride as the acceptor. The kinetics of F?rster resonance energy transfer (FRET) between the dyes is sensitive to the donor-acceptor distance, allowing us to obtain the binding distribution of the dyes at the nanoparticle surface. For the unmodified nanoparticles, we found a dye distribution that corresponds to an average interface thickness of delta = (5.2 +/- 0.2) nm. For the samples containing 13 mol % and 30 mol % of TMS groups in the outer shell we obtained broader interfaces, with widths of delta = (6.2 +/- 0.2) nm and delta = (6.5 +/- 0.1) nm respectively. This broadening of the distribution with the surface modification is interpreted in terms of the increase in free volume of the shell caused by the TMS groups. Finally, we studied the effect of temperature on the water-polymer interface fuzziness, in order to evaluate the accessibility of the TMS groups during the sol-gel synthesis of nanostructured hybrid materials.     

Preparation of silver nanoparticles in solution from a silver salt by laser irradiation

A new method is proposed for the fabrication of a well-defined size and shape distribution of silver nanoparticles in solution; the method employs direct laser irradiation of an aqueous solution containing a silver salt and a surfactant in the absence of reducing agents.     

溶剂热法制备银纳米晶

以聚乙烯吡咯烷酮(PVP)作为表面活性剂,利用乙二醇溶剂热法成功制备了银纳米颗粒;利用场发射扫描电子显微镜(FE-SEM)、透射电子显微镜(TEM)、X射线衍射(XRD)分析了样品的形貌和晶体结构,并考察了溶剂组成等因素对银纳米颗粒形貌的影响.研究结果表明所得银纳米晶粒径均一,直径约为90nm;增大PVP的加入量会降低产物的粒径,溶剂中水的引入会影响银纳米晶的形貌.     

Preparation of antibacterial polyimide films containing silver nanoparticles

Polyimide/silver composite films were successfully prepared by in situ polymerization. A precursor, AgNO₃ was used as the source of the silver nanoparticles. The structure and morphology of resulting films were characterized by FTIR spectroscopy, X-ray diffraction (XRD) and scanning electron microscopy (SEM). Consequently, the silver nanoparticles were well dispersed in polyimide matrix. Meanwhile, thermal properties from thermal gravimetric analyses (TGA) and mechanical properties from tensile test which confirmed composites were kept good performance as compared to pure polyimide. In addition, the antimicrobial activity of polyimide/silver composite films against three different bacteria, B. subtilis, S. aureus, and E. coil, illustrated excellent activity. This composite is potential useful as antimicrobial material with good thermal performance in a wide variety of biomedical and general use applications.     

Preparation of silver nanoparticles with controlled particle size

Silver colloids show different colors due to light absorption and scattering in the visible region based on plasmon resonance. The resonance wavelength depends on particle size and shape. Here we report chemical reduction methods for preparation of silver nanoparticles exhibiting multicolor in aqueous solutions. Depending on chemical conditions the obtained nanoparticles are different regarding size and morphology.In order to investigate the relationship between size, stability and color of silver colloids we obtained silver nanoparticles in aqueous solutions using different reducing agents. The effect of polyvinyl pyrrolidone (PVP) and polyvinyl alcohol (PVA) on stabilization of obtained silver colloids was investigated. We have also studied the effect of silver precursor and its concentration on the formation of stable silver colloids.UV-VIS spectrum for silver colloids contains a strong plasmon band near 410 nm, which confirms silver ions reduction to Ag° in the aqueous phase. The formation of metal silver was also confirmed by powder X-ray diffraction (XRD) analysis. The diameter size of silver nanoparticles was in the range from 5 nm to 100 nm     

Preparation,characterization and catalytic activity of biomaterial-supported copper nanoparticles

Synthesis of copper nanoparticles was carried out with nanocrystalline cellulose (NCC) as a support by reducing CuSO₄·5H₂O ions using hydrazine. Ascorbic acid and aqueous NaOH were also used as an antioxidant and pH controller, respectively. The synthesized copper nanoparticles supported on NCC (CuNPs@NCC) were characterized by UV–vis, XRD, TEM, XRF, TGA, DSC, N₂ adsorption-desorption method at 77 K and FTIR. The UV–vis confirmed the formation and stability of the CuNPs, which indicated that the maximum absorbance of CuNPs@NCC was at 590 nm due to the surface plasmon absorption of CuNPs. Morphological characterization clearly showed the formation of a spherical structure of the CuNPs with the mean diameter and standard deviation of 2.71 ± 1.12 nm. Similarly, XRD showed that the synthesized CuNPs@NCC was of high purity. The thermal analysis showed that the CuNPs@NCC exhibited better thermal behaviors than NCC. BET surface area revealed that the N₂ adsorption–desorption isotherms of CuNPs@NCC featured a type IV isotherm with an H3 hysterisis loop. This chemical method is simple, cost effective, and environmentally friendly. Compared to NCC-supported CuNPs and unsupported CuNPs, the as-prepared CuNPs@NCC exhibit a superior catalytic activity and high sustainability for the reduction of methylene blue with NaBH₄ in aqueous solution at room temperature. The CuNPs@NCC achieved complete reduction of MB with completion time, rate constant and correlation coefficient (R ²) of 12 min, 0.7421 min^?1 and 0.9922, respectively.